Installation Precautions And Fault Diagnosis Of Thermal Expansion Valve
Aug 20, 2025
Installation Precautions And Fault Diagnosis Of Thermal Expansion Valve
Small cold storage typically has a capacity of less than 100 tons. The refrigerant used in the compressor is usually R22. Low-temperature cold storage typically uses semi-hermetic compressors, while high-temperature cold storage typically uses fully hermetic compressors. The cold storage evaporator can use either a ducted or air cooler system.
I. Summary of Experience in Installing Thermal Expansion Valves in Small Cold Storages
1. Before installation, check that the temperature sensor is intact.
2. The expansion valve must be installed close to the evaporator, with the valve body mounted vertically.
3. During installation, ensure that the liquid in the temperature sensor remains within the package. Therefore, the package should be installed lower than the valve body.
4. Whenever possible, install the temperature sensor on the horizontal return air pipe at the evaporator outlet, generally at least 1.5 meters away from the compressor intake.
5. Avoid installing the temperature sensor on return pipes where liquid has accumulated.
6. If the evaporator outlet is equipped with a gas-liquid exchanger, the temperature sensor is generally installed at the evaporator outlet, before the heat exchanger.
7. The temperature sensor is typically placed on the evaporator return air pipe, tightly wrapped against the pipe wall, and any contact points should be cleaned.
8. If the return air pipe diameter is less than 25 mm, the temperature sensor can be tied to the top of the return pipe. If the diameter is greater than 25mm, it can be taped at a 45-degree angle on the underside of the return pipe to prevent oil accumulation at the bottom of the pipe from affecting the temperature sensing package.
II. Small Cold Storage Thermal Expansion Valve Debugging Techniques
1. Verify the superheat at the evaporator outlet using a thermometer or by observing the suction pressure.
2. If the expansion valve superheat is set too low or the liquid supply is too high, the adjusting rod should be turned clockwise half a turn or one turn to increase the spring force, reduce the valve opening, and reduce the refrigerant flow. The adjusting rod should not be turned too many times at a time; one turn of the adjusting rod changes the superheat by approximately 1-2 degrees.
3. Experience in Expansion Valve Adjustment: Adjust the adjusting rod to adjust the valve opening so that frost or condensation forms on the outside of the evaporator return pipe. For refrigeration units with an evaporating temperature below 0°C, if frost forms and you feel a sticky, cold sensation when you touch it, the valve opening is appropriate. For evaporating temperatures above 0°C, the condensation level can be used to determine the appropriate valve opening. 4. Proper expansion valve commissioning directly impacts cold storage cooling performance and energy savings. Slow cold storage cooling is often due to improper expansion valve adjustment. According to the thermodynamic properties of refrigerants, lower pressure corresponds to lower temperatures, while higher pressure corresponds to higher temperatures. Adjustment of the expansion valve is crucial. A narrower expansion valve opening reduces refrigerant flow and lowers pressure. A wider expansion valve opening increases refrigerant flow and higher pressure.
III. Expansion Valve Commissioning Precautions
If the expansion valve outlet pressure is too low, the corresponding evaporation pressure and temperature are also too low. However, the reduced flow and pressure entering the evaporator slow the evaporation rate, reducing cooling capacity per unit volume and time, and lowering cooling efficiency. Conversely, if the expansion valve outlet pressure is too high, the corresponding evaporation pressure and temperature are also too high. This increases both the flow and pressure entering the evaporator. Excessive liquid evaporation causes overly humid gas, or even liquid, to be drawn into the compressor, causing a wet stroke (liquid hammer) that can cause compressor malfunction, adverse operating conditions, and even damage the compressor. Therefore, the opening degree of the expansion valve should be adjusted according to the current warehouse temperature, that is, adjusted at the pressure corresponding to the warehouse temperature.
Common faults include filter blockage and temperature sensor leakage. These can lead to sluggish regulation, loss of control, or even inability to adjust. Frost forms on the expansion valve inlet or valve cover, causing the liquid inlet pipe to be colder than normal, or even condensation. The compressor's suction pressure is lower than the corresponding pressure at storage temperature, the machine's operating and exhaust temperatures are high, and the cooling temperature drops slowly or even fails to drop. This is likely due to a clogged expansion valve filter, dirt, or ice blockage.
